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Date: Wed, 12 Aug 2015 16:40:25 +0200
From: Oleg Nesterov <oleg@redhat.com>
To: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: "Kirill A. Shutemov" <kirill@shutemov.name>,
        Andrew Morton <akpm@linux-foundation.org>,
        Kees Cook <keescook@chromium.org>, David Howells <dhowells@redhat.com>,
        linux-kernel@vger.kernel.org, Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@kernel.org>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Rik van Riel <riel@redhat.com>,
        Vladimir Davydov <vdavydov@parallels.com>,
        Ricky Zhou <rickyz@chromium.org>, Julien Tinnes <jln@google.com>
Subject: Re: [PATCH] user_ns: use correct check for single-threadedness
Message-ID: <20150812144025.GA11979@redhat.com>
References: <20150728171500.GA2871@www.outflux.net> <20150728143504.5aa996ba5955522a19c2d5f1@linux-foundation.org> <20150728221111.GA23391@node.dhcp.inet.fi> <20150805172356.GA20490@redhat.com> <87wpx9sjhq.fsf@x220.int.ebiederm.org> <87614tr2jd.fsf@x220.int.ebiederm.org> <20150806130629.GA4728@redhat.com> <20150806134426.GA6843@redhat.com> <87egj9cnk3.fsf@x220.int.ebiederm.org>
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On 08/11, Eric W. Biederman wrote:
>
> Oleg Nesterov <oleg@redhat.com> writes:
>
> >> Then why we can't simply check thread_group_empty() == T ? Why should we
> >> worry about CLONE_SIGHAND at all?
> >
> > The same for clone() actually... I forgot why we decided to check
> > CLONE_SIGHAND, iirc I suggested CLONE_THREAD initially then we switched
> > to CLONE_SIGHAND "just in case", to make it as strict as possible.
>
> I do agree that making the test be for CLONE_THREAD is safe, makes
> sense, and is less confusing than what we have now.x

Good,

> > How about the patch below?
> >
> > (note that the "or parent" part of the comment is wrong in any case).
>
> It was correct.

Yes, I know,

> You failed to removed it when you removed CLONE_PARENT
> from that test.

Cough... it was you ;) 1f7f4dde5c945f41a7abc2285be43d918029ecc5
"fork:  Allow CLONE_PARENT after setns(CLONE_NEWPID)".

Oleg.